Ceramic Matrix Composite Structure having Fluted Core and Method for Making the Same
A ceramic matrix composite structure includes a load carrying fluted core formed from a ceramic matrix composite. The fluted core includes a plurality of nested flute members laminated between a pair of ceramic matrix composite facesheets. The flute members are fabricated by wrapping ceramic resin fabric around a mandrel, curing the flute members and then removing the mandrels. The structure may include reinforced areas in which the facesheets are laminated directly together to receive fasteners for mounting the structure. The structure may include both flat and curved portions.
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This disclosure generally relates to ceramic matrix composite structures, and deals more particularly with a sandwich construction having a load-carrying fluted core, as well as a method for making the structure.
BACKGROUNDCeramic matrix composite (CMC) structures are often used in aerospace and other applications because of their ability to withstand relatively high operating temperatures. For example, CMC structures may be used to fabricate parts subjected to high temperature exhaust gases in aircraft applications. Various CMC's have been employed to fabricate either monocoque structures or structures that employ a combination of tile and/or foam sandwich constructions, but neither of these types of structures may be well suited for carrying loads. In the case of CMC monocoques, the materials must be relatively thick in order for the structure to carry a load, but the additional material thickness adds weight to the aircraft. CMC tile/foam sandwich materials have not been widely used in load carrying applications, in part because of their relatively weak core materials.
Accordingly, there is a need for a CMC structure that is relatively light weight, but yet has sufficient structural strength to be self-supporting and capable of carrying loads. It would also be desirable to provide a CMC structure that may be formed into various shapes, including those possessing curvature. Additionally, it would be desirable to provide a simple, cost effective method of fabricating these CMC structures. Embodiments of the disclosure are intended to satisfy these needs.
SUMMARYEmbodiments of the disclosure provide a CMC sandwich construction that allows fabrication of structures having various geometries, including curved surfaces and reinforced features that allow the structures to be mounted using the fasteners. The disclosed embodiments employ a CMC sandwich incorporating a fluted core formed of a CMC that strengthens the structure and allows it to carry loads. The CMC fluted core structure may be fabricated using commercially available materials and well known polymer layup techniques to produce a wide variety of parts, components and assemblies, especially those used in the aircraft industry.
According to one disclosed embodiment, a ceramic matrix composite structure is provided, comprising a pair of spaced apart, CMC facesheets, and a load carrying core between at least a portion of the facesheets, wherein the core includes CMC flute members. The flute members may form a closed cell that may or may not be filled with any of a variety of high temperature materials. The flute members may be formed of ceramic matrix composite material having a wall cross section in the shape of an isosceles trapezoid, or other geometric shape. The flute members are arranged in side-by-side, nested relationship between the CMC facesheets.
According to another embodiment, a CMC sandwich is provided, comprising a pair of spaced apart, CMC facesheets, and a plurality of CMC flutes between at least a portion of the facesheets for transmitting compression and shear loads between the facesheets. The facesheets may include both flat and curved sections, and the flutes may include walls conforming to the curvature of the facesheets. Portions of the facesheets may be directly laminated together to provide a reinforced structural area suitable for being pierced by mounting fasteners.
According to a method embodiment of the disclosure, CMC structures may be fabricated by a method comprising the steps of: forming a plurality of flutes using a CMC; placing the flutes between a pair of CMC facesheets; and, bonding the flutes to the facesheets. The flutes may be formed by wrapping ceramic matrix prepreg fabric over a tool and then curing the prepreg. The tool may be either a permanent tool that is later removed, or a rigid, fugitive foam.
According to another method embodiment, a CMC sandwich for use in aerospace structures may be fabricated by a method comprising the steps of: forming a load carrying structural core using CMC material; placing the core between a pair of CMC facesheets, and fusing the facesheets with the core. The core may be formed by fabricating a plurality of flutes, placing the flutes in nested, side-by-side relationship, and then laminating the flutes between the facesheets.
Other features, benefits and advantages of the disclosed embodiments will become apparent from the following description of embodiments, when viewed in accordance with the attached drawings and appended claims.
Referring first to
Each of the facesheets 12, 14 may comprise multiple layers or plies of ceramic fiber material impregnated with a matrix material or “prepreg”. As used herein, the term “ceramic” refers to the conventionally known and commercially available ceramic materials that are fabricated in a fiber form. The ceramic fibers may include, but are not limited to, silicon carbide, silica, TYRANNO®, alumina, aluminoborosilicate, silicon nitride, silicon boride, silicon boronitride, and similar materials.
The load carrying core 16 may function to transmit compressive, tensile and shear loads between the facesheets 12, 14, allowing the CMC structure 10 to be both self-supporting and load carrying. The CMC structure 10 is particularly well suited to high temperature applications since all of the composite materials in the CMC structure 10 are ceramic-based. The core 16 comprises a plurality of elongate flute members 18 which are bonded together in nested, side-by-side relationship between the facesheets 12, 14. The flute members 18 may be hollow, or may be filled with any of a variety of ceramic materials, including, without limitation, rigid ceramic tile or foam, ceramic felt, other fibrous ceramic insulation (soft or rigid), monolithic ceramics, etc.
One rigid foam suitable for use in filling the flute members 18 is disclosed in U.S. Pat. No. 6,716,782 issued Apr. 6, 2002 and assigned to The Boeing Company. The rigid foam insulation described in this prior patent is a combination of ceramic fibers which are sintered together to form a low density, highly porous material with low thermal conductivity. This foam exhibits high tensile strength and good dimensional stability. As used herein, “high temperature” material is generally intended to refer to temperatures above which polymeric materials exhibit diminished capacity.
In the particular embodiment illustrated in
The walls 18a, 18b form bridging elements that provide load paths between the facesheets 12, 14. As best seen in
The walls 18b of adjacent flute members 18 may be bonded together in face-to-face contact. The intersection of adjacent flute members 18 and facesheets 12, 14 form voids that may be filled with fillers 20 in the form of elongate “noodles” that have a cross sectional shape matching that of the void; in the illustrated example, the voids, and the noodle fillers 20 are triangular in cross section. The noodle fillers 20 may be made with CMC prepreg, tape, tows, or filaments, and function to more evenly distribute and transmit loads between the facesheets 12, 14.
Referring now to
Multiple flat or curved structures 10, 10a may be bonded together or interconnected using, for example, a bayonet-like interconnection shown in
A method for fabricating the structures 10, 10a is illustrated in
Next, at step 32, the wrapped flute members 18 are assembled together by nesting them in side-by-side relationship, following which the assembled flute members 18 are cured at step 34 normally at elevated temperature and pressure. At step 36, the prepreg noodle fillers 20 are installed in the voids between adjacent flute members 18.
At step 38, the facesheets 12, 14 are applied to each side of the assembled flute members 18, and the resulting sandwich assembly is then cured in the normal manner which may involve, for example, placing the sandwich assembly in an autoclave (not shown). The facesheets 12, 14 may be formed using a layup of woven fabric prepreg, tape/tow placement or filament winding.
Following the curing step at 40, the mandrels are removed at step 42 if they comprise permanent tooling. Otherwise the fugitive foam mandrels are left in place, and the entire sandwich assembly is post-cured at elevated temperatures, as shown at step 44. Depending on the type of rigid foam used as the mandrel tool, the elevated temperatures during the post-curing step 44 may be sufficient to incinerate the mandrel tools. Subsequently, non-destructive inspection techniques such as thermography or CT scanning can be used at step 46 (see
Where a CMC structure 10a is to be fabricated having curved sections, appropriate layup tooling (not shown) may be provided for forming the facesheets 12a, 14a into the desired shapes. The flute members 18 may be filled with a flexible, organic fugitive foam mandrel (not shown) so that the flute members 18 conform to the curved shape of the facesheets 12a, 14a. The fugitive foam mandrel may be either be washed out or pyrolyzed during the CMC post curing step 44.
The embodiments of the disclosure described above may be described in the context of an aircraft manufacturing and service method 50 as shown in
Each of the processes of method 50 may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include without limitation any number of aircraft manufacturers and major-system subcontractors; a third party may include without limitation any number of venders, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on.
As shown in
Apparatus and methods embodied herein may be employed during any one or more of the stages of the production and service method 50. FDr example, components or subassemblies corresponding to production process 56 may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft 80 is in service. Also, one or more apparatus embodiments, method embodiments, or a combination thereof may be utilized during the production stages 56 and 58, for example, by substantially expediting assembly of or reducing the cost of an aircraft 80. Similarly, one or more of apparatus embodiments, method embodiments, or a combination thereof may be utilized while the aircraft 80 is in service, for example and without limitation, to maintenance and service 64.
Although the embodiments of this disclosure have been described with respect to certain exemplary embodiments, it is to be understood that the specific embodiments are for purposes of illustration and not limitation, as other variations will occur to those of skill in the art.
Claims
1. A ceramic matrix composite structure, comprising:
- a pair of spaced apart, ceramic matrix composite facesheets; and,
- a load carrying core between at least a portion of the facesheets, the load carrying core including ceramic matrix composite flutes.
2. The ceramic composite structure of claim 1, wherein:
- at least certain of the flutes include a closed cell filled with ceramic foam.
3. The ceramic composite structure of claim 2, wherein the cell includes a continuous wall defined by compacted multiple plies of ceramic fiber reinforced resin.
4. The ceramic composite structure of claim 1, wherein each of the facesheets includes compacted multiple plies of ceramic fiber reinforced resin.
5. The ceramic composite structure of claim 1, wherein:
- the flutes are arranged in side-by-side relationship and define voids therebetween, and
- the core further includes filler strips filling the voids.
6. The ceramic composite structure of claim 1, wherein:
- at least a section of each of the facesheets is curved, and
- the flutes conform to the curvature of the facesheet section.
7. The ceramic composite structure of claim 1, further comprising a solid structural core between another portion of the facesheets.
8. The ceramic composite structure of claim 1, wherein each of the flutes has a cross sectional shape forming substantially an isosceles trapezoid.
9. A ceramic matrix composite sandwich, comprising:
- a pair of spaced apart, ceramic matrix composite facesheets; and,
- a plurality of ceramic matrix composite flutes between at least a portion of the facesheets for carrying compression and shear loads between the facesheets.
10. The ceramic matrix composite sandwich of claim 9, wherein each of the flutes includes four walls forming substantially an isosceles trapezoid in cross section.
11. The ceramic matrix composite sandwich of claim 9, wherein:
- the facesheets include a flat section and a curved section, and
- the flutes include walls conforming to the curvature of the facesheets in the curved section.
12. The ceramic matrix composite sandwich of claim 9, wherein the flutes are filled with a rigid ceramic foam.
13. The ceramic matrix composite sandwich of claim 9, wherein portions of the facesheets are laminated together.
14. The ceramic matrix composite sandwich of claim 9, further comprising a solid ceramic core bonded between a portion of the facesheets.
15. The ceramic matrix composite sandwich of claim 9, wherein each of the flutes includes:
- a first pair of spaced apart walls respectively engaging the facesheets, and
- a second part of spaced apart walls connected to the first pair of walls and extending between the facesheets.
16. The ceramic matrix composite sandwich of claim 9, wherein: core further includes foam insulation filling the space between the first and second composite sheets.
- the flutes are nested together and include voids therebetween, and
17. A method of fabricating a ceramic matrix composite structure, comprising the steps of:
- (A) forming a plurality of flutes using a ceramic matrix composite;
- (B) placing the flutes formed in step (A) between a pair of ceramic matrix composite facesheets; and
- (C) bonding the flutes to the facesheets.
18. The method of claim 17, wherein step (A) includes:
- wrapping ceramic matrix prepreg fabric over a tool, and curing the prepreg.
19. The method of claim 18, wherein step (A) further includes forming the tool by shaping a rigid foam into a mandrel.
20. The method of claim 18, wherein step (A) further includes incinerating the foam after the prepreg has been cured.
21. The method of claim 17, wherein step (A) includes:
- arranging the flutes in side-by-side nested relationship, and
- curing the arranged flutes.
22. The method of claim 17, further comprising the step of installing a filler in voids between adjacent flutes and the facesheets.
23. The method of claim 17, further comprising the step of:
- (D) laminating together portions of the facesheets.
24. The method of claim 17, further comprising the steps of:
- (D) placing a solid ceramic core between a portion of the facesheets; and,
- (E) bonding the portion of facesheets to the ceramic core.
25. The method of claim 17, wherein step (C) is performed by co-curing the facesheets and the flutes
26. An aircraft assembly using the structure fabricated in claim 17.
27. The method of claim 17, further comprising the step of:
- (D) designing an aircraft assembly incorporating the structure.
28. The method of claim 17, further comprising the step of:
- (D) procuring the material used to fabricate the structure.
29. The method of claim 17, wherein fabricating the structure forms part of an operation for manufacturing an aircraft assembly.
30. A method of fabricating a ceramic matrix composite sandwich for use in aerospace structures, comprising the steps of:
- (A) forming a load bearing structural core using ceramic matrix composite material;
- (B) placing the core between a pair of ceramic matrix composite facesheets; and,
- (C) fusing the facesheets with the core.
31. The method of claim 30, wherein step (A) includes:
- fabricating a plurality of flutes, and
- placing the flutes in side-by-side relationship.
32. The method of claim 31, wherein the flutes are fabricated by:
- wrapping ceramic matrix prepreg over a tool, and
- curing the prepreg.
33. The method of claim 30, wherein step (A) includes placing fillers in voids between the face sheets and the core.
34. The method of claim 30, wherein step (C) is performed by co-curing the core and the facesheets.
Type: Application
Filed: Jun 28, 2007
Publication Date: Jan 1, 2009
Applicant:
Inventors: Leanne L. Lehman (Aliso Viejo, CA), John R. McCann (Newport Beach, CA)
Application Number: 11/770,035
International Classification: B32B 3/20 (20060101);